Cell type-specific abnormalities of central nervous system in myotonic dystrophy type 1

Abstract

Myotonic dystrophy type 1 is a multisystem genetic disorder involving the muscle, heart and CNS. It is caused by toxic RNA transcription from expanded CTG repeats in the 3′-untranslated region of DMPK, leading to dysregulated splicing of various genes and multisystemic symptoms. Although aberrant splicing of several genes has been identified as the cause of some muscular symptoms, the pathogenesis of CNS symptoms prevalent in patients with myotonic dystrophy type 1 remains unelucidated, possibly due to a limitation in studying a diverse mixture of different cell types, including neuronal cells and glial cells. Previous studies revealed neuronal loss in the cortex, myelin loss in the white matter and the presence of axonal neuropathy in patients with myotonic dystrophy type 1. To elucidate the CNS pathogenesis, we investigated cell type-specific abnormalities in cortical neurons, white matter glial cells and spinal motor neurons via laser-capture microdissection. We observed that the CTG repeat instability and cytosine–phosphate–guanine (CpG) methylation status varied among the CNS cell lineages; cortical neurons had more unstable and longer repeats with higher CpG methylation than white matter glial cells, and spinal motor neurons had more stable repeats with lower methylation status. We also identified splicing abnormalities in each CNS cell lineage, such as DLGAP1 in white matter glial cells and CAMKK2 in spinal motor neurons. Furthermore, we demonstrated that aberrant splicing of CAMKK2 is associated with abnormal neurite morphology in myotonic dystrophy type 1 motor neurons. Our laser-capture microdissection-based study revealed cell type-dependent genetic, epigenetic and splicing abnormalities in myotonic dystrophy type 1 CNS, indicating the significant potential of cell type-specific analysis in elucidating the CNS pathogenesis.

Analysis of splicing abnormalities in the white matter of myotonic dystrophy type 1 brain using RNA-sequence

“…Third, the difference in the number of repeats between the GM and WM could propel abnormal splicing. Indeed, Nakamori et al measured the CTG repeat length in the neurons of the GM and glial cells of the WM in the anterior temporal lobe and reported that neurons of the GM had significantly longer repeats [36]. In the present study, the number of repeats in the GM and WM was not statistically significantly different; however, the number of repeats in the GM was extended in all the samples.…”

“…Accumulation of RNA foci and splicing abnormalities have also been reported in the oligodendrocytes of mice [35]. Many mis-splicing events have been found in the WM glial cells of patients with DM1, and some of the mis-splicing events are more prominent in the WM glial cells than in the GM neurons [36]. Thus, splicing abnormalities in the glial cells, such as astrocytes and oligodendrocytes, could be related to the differences in splicing defects between the GM and WM.…”

Increased FAN1 expression by mRNA-LNP attenuates CAG repeat expansion in Huntington patients’ iPSC-derived astrocytes

“…Although historical studies suggest a strictly neuronal pathology in patient’s brains due to triplet repeat expansions, other groups have demonstrated that the expression of Htt with expanded CAG repeats in mouse astrocytes manifest functional atrophy (52). In addition, a recent study indicates white matter glial cells in CNS of myotonic dystrophy type 1 (DM1) patients present unstable and longer repeats (61) relative to healthy. Thus, the overall weight of evidence shows astrocytes are involved in repeat expansion disorders.…”

Expanded‐repeat‐RNA‐mediated disease mechanisms in myotonic dystrophy

“…However, laser capture microdissection, which discriminates and provides pure cell type populations of targeted cells from specific microscopic regions of interest, enables the identification of region and cell type‐specific splicing abnormalities in DM1 CNS. By using this technique, splicing abnormalities involved in neuronal differentiation of DM1 motor neurons have been identified 17 …”

“…By using this technique, splicing abnormalities involved in neuronal differentiation of DM1 motor neurons have been identified. 17 There have been reports of suggested pathogenic mechanisms other than splicing abnormalities in RNA metabolism of DM; the loss of MBNL1 has additional effects on gene expression through the regulation of alternative polyadenylation, mRNA transport, and microRNA biogenesis. [18][19][20] The increase in CELF1 expression may affect mRNA stability and translation.…”